In the undersea repeaters of a cable transmission link having optical fibers, the access cables to a repeater are constituted by respective metal tubes sheathed in insulating material and containing the optical fibers. A repeater is provided with two access cables, one at each end. The description below relates to the items associated with one of the ends of a repeater, it being understood that the same items are identically disposed at the other end.
Such a connection is described in French Pat. No. 86 15874 filed Nov.14, 1986. The access cable is provided with a sealing device which provides longitudinal sealing in the event of the cable breaking, thereby preventing water penetrating into the repeater and destroying it. In the event of accidental traction on the access cable, that device is effective only if the cable breaks at a point situated upstream from the sealing device relative to the repeater, and it is not effective if the break is between the sealing device and the repeater.
That is why provision has been made, as described in the above-mentioned French patent, for a mechanical fuse which, in the event of a force exceeding a given value, causes the cable to break upstream from the longitudinal sealing device.
That fuse is constituted by a plug fitted over and fixed to one end of the tube and including the optical fibers of the access cable, a ring fixed to a cable head and engaged on the plug, and a set of pins holing the ring and the plug together transversely. Under the effect of traction greater than the given value, the plug is ejected from the wall of the cable head, thereby breaking the fibers upstream from the sealing device, inside the tube or inside the cable head.
The metal tube in an access cable is obtained by metal drawing, so access cables present wide dispersion in their resistance to traction. In order to ensure that the mechanical fuse is effective regardless of which access cable is used, the fuse is designed to break the connection at a traction value that is lower than the minimum traction strength tolerance that can be accepted for a cable, and for a tube of given transverse dimensions.
The characteristics to be taken into account for the function attributed to the fuse make it relatively fragile by construction. During repeater manufacture, the operation of fuse assembly runs the risk of accidental breakage. This risk increases with decreasing outside diameter of the tube of the access cable (for substantially identical inside diameter, as is becoming the case in more recent connections). In order to ensure that it remains effective, matching the fuse to these new dispositions would require its sensitivity to be increased, thereby reducing the strength of the pins, and thus making it too fragile and ill-suited to the cycle during which the housings of equipment to be submerged are prepared.
An object of the present invention is to provide a connection which presents no risk of breaking accidientally during assembly operations in the factory, regardless of the traction strength characteristics of the tub in the cable concerned.
Another object of the invention is to provide a connection which, in the event of traction greater than a predetermined value being exerted on the cable, reliably ensures that the access cable breaks together with all of the optical fibers it contains upstream from the longitudinal sealing device.